Treatment of characteristic signals of a colour television picture



Nov. 10, 1970 R. FONTENIT TREATMENT OF CHARACTERISTIC SIGNALS OF A COLOUR TELEVISION PICTURE Filed July 14,

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United States Patent 3,539,711 TREATMENT OF CHARACTERISTIC SIGNALS OF A COLOUR TELEVISION PICTURE Roger Fontenit, Paris, France, assignor to CSF-Compagnie Generale de Telegraphic Sans Fil, a corporation of France Filed July 14, 1967, Ser. No. 653,503 Claims priority, application France, July 29, 1966,

71,396 Int. Cl. H04n 9/32 US. Cl. 1785.2 4 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to colour television.

More particularly it relates to an improvement to the channels through which the characteristic signals of a colour television picture (for example, the primary colour R, G and B or chrominance signals), are transmitted and wherein they are treated. This invention makes it possible to eliminate distortions in the coloured picture caused by a dissymmetry of such channels. This object is achieved with a great economy of means as compared to conventional arrangements.

In known systems, the information relative to each colour is treated in separate channels. In order to preserve the essential characteristics of this information, it is therefore necessary that the corrections or modifications to which each information is subjected either intentionally or accidentally should be exactly the same for all of these channels.

It is an object of this invention to make all the colour information pass through the same channel, which results in a simplification of the equipment, while preserving the characteristics of the colour information, without regard to the state of the transmission channel.

In the following description, the invention will be considered by way of non-limitative only, as applied to camera circuits wherein the treatment of primary colour signals comprises, for example the gamma correction of the three primary colours, the variation of the signal amplitude and fixing the zero level of these signals.

Another advantage of the system is that it makes it possible to control simultaneously the amplitude of all the three colour signals, since the process is characterized by a non-additive mixing of the primary signals.

Any given zone of a picture is characterized by its chromaticity which is a function only of the ratios between the amplitudes of different primary colour signals, and by its luminance which is a function of the value of these amplitudes, so that a white zone has, by definition, a chromaticity characterized by the relation: R=B=G.

If the luminance of this white Zone is varied, which is efifected by varying the amplitudes of the signals, R. B and G, whilst maintaining the above relation, one obtains a scale of values corresponding to zones ranging from white to black. These zones will be referred to by the term achromatic zones.

When a camera analyzes achromatic zones, the quality of the signals R, B and G must be maintained without regard to the luminance of this zone, since otherwise, in the "Ice reproduction, this achromatic zone will tend to assume the colour of the strongest primary colour signal. This defect is especially undesirable and visible in achromatic zones between the white and the black.

It is therefore necessary that the three video channels should be as similar as possible. However, it is difiicult to obtain the similarity of the characteristics of three video channels and even more difficult to maintain this similarity in time and in exploitation.

An object of this invention is to overcome these drawbacks.

According to the invention there is provided a system for the treatment and the transmission of at least two characteristic signals of a colour television picture comprising: multiplexing means having at least two inputs for receiving said characteristic signals and an output for supplying a resultant signal; a single channel connected to said outputs for the treatment and the transmission of said resultant signal, said channel having an output for supplying a treated resultant signal; and demultiplexing means, connected to said output of said channel and having at least two outputs for supplying treated characteristic signals, corresponding to said characteristic signals.

For a better understanding of the invention, and to show how the same may be carried into effect reference will be made to the drawing accompanying the following description and wherein:

FIG. 1 is a block diagram of one embodiment of the improvement according to the invention wherein time multiplexing is used;

FIGS. 2 and 3 show explanatory diagrams.

As already mentioned the invention will be described by way of example withflparticular reference to its application to a colour television camera comprising a high definition tube for providing a wide-band luminance signal.

FIG. 1 shows an arrangement 1, such as that used in a television camera, for elaborating primary colour signals, of any known type, capable of respectively providing at its outputs 11, 12, 13 and 14 the non-corrected primary colour signals R, G and B and a wide-band high definition signal Y. Such a device may comprise, for example:

(a) four tubes supplying signals R, G, B and the luminance signal Y;

(b) or three tubes providing respectively signals R, B and Y, the third colour signal being reconstituted by means of the preceding signals.

The outputs 11, 12 and 13 are connected, respectively, to three electronic gates 2, 3 and 4, having control inputs 20, 30 and 40. The outputs of the gates 2, 3 and 4 are connected together to the input of a correcting and amplifying circuit 5, which is a single channel carrying out the treatment of the primary colour signals. This circuit may be for example a circuit of known type performing the functions mentioned above and whose output is connected to the inputs of three electronic gates 2, 3' and 4', having control inputs 20', 30' and 40. The respective outputs 8, 9 and 10 of the gates 2, 3', 4 form, with the output 14, the utilization outputs of the camera. A pilot oscillator 6 is connected to a circuit 7 forming sampling pulses and having outputs 72, 73 and 74. The output 72 is connected to the control inputs 20 and 20', the output 73 to the control inputs 30 and 30, and the output 74 to the control inputs 40 and 40. The operation of the system will now be described with further reference to the diagrams shown in FIG. 2.

The oscillator 6 serves as a clock for the system and supplies oscillations with a sufficiently high frequency compared with the highest frequency of the frequency band occupied by the signals R, G and B. The oscillator 6 feeds the circuit 7 forming the sampling pulses. The

latter supplies at its outputs 72, 73 and 74, respectively, the pulses shown in FIGS. 2a, 2b and 20. According to the circuit 7 used, these pulses may have the same frequency as the oscillator 6, or a frequency double the frequency of that oscillator.

In a camera with four signals, whose colour channels are limited to 2 mc./s, a pilot frequency of mc./ s. can be used. The pulses applied to the output 73 are delayed by T =T/ 3 relative to those supplied to output 72' where T is the period of these pulses. Similarly, the pulses supplied to the output 74 are delayed by T =2T 3 relative to the pulses applied to the output 72. The signals of the primary colours R, G, B are therefore sampled by the gates 2, 3 and 4 which are kept open during the duration of the pulses controlling them. The resulting signal, i.e., the sum of the three samplings, is applied to the input of the single circuit 5 which effects the various corrections necessary.

It is also possible to envisage a sampling by a signal having three times the preceding frequency, which eliminates the delay of the three groups of sampling signals.

The gates 2, 3 and 4' which are synchronous with the gates 2, 3 and 4, respectively, make it possible to extract from the corrected signal the corrected red, green and blue signals. Hence, since the corrections are effected by a single circuit acting on all three signals, it is certain that they are strictly the same, and even if the characteristics of this circuit change with time or during use, the same ratio is maintained between the amplitudes of the corrected signals R, G and B, which is the desired result.

It is easy to deduce from the operation of the camera that the frequency of the oscillator 6 must be sufliciently high, compared with the highest frequency of the band occupied by the signals R, G and B, so that the corrected signals, collected at the outputs 8, 9 and 10 reproduce with sufiicient accuracy (taking of course into account the corrections) the contents of the non-corrected signals R, G and B.

Of course, the order of the primary colour signals in the resulting signal is irrelevant.

The invention has been described with reference to a camera including a high definition tube providing a luminance signal.

The invention is of course also aplicable to the case where the luminance signal is formed by an adequate linear combination of gamma corrected primary colour signals provided by the analyser tubes. However, in this case it is preferable, in order to have a luminance signal with a sufficient definition, to increase the sampling rate in so far as the signal which matters most for the formation of a composite luminance signal is concerned, i.e., the green signal G which partakes to the extent of 59 percent in the formation of the composite signal Y. Thus as shown in FIG. 3 the number of signal G samples may be double that of signal R and B samples. This is readily achieved by using for signals R and B sampling pulses having the frequency of oscillator 6 and shifted in time, while using for signal G pulses having a frequency double that of the oscillator 6.

In the described embodiment, a time multiplex has been used. Obviously the invention is not restricted to this type of multiplexing.

More particularly, according to the invention, the primary colour signals may be, for example, multiplexed in frequency. To this end, each signal modulates in amplitude a suitably selected subcarrier. These subcarriers are preferably such that their respective spectrum components occupy spectrum parts not occupied by the spectrum components of the other modulated subcarriers so as to reduce appreciably the width of the total spectrum and, therefore, of the pass band necessary for the common channel. At the output of this channel, a demodulating system makes possible the separation of the different primary colour signals. Naturally, without departing from the principle of the invention, it is possible to use, for example, phase multiplexing in which one or more subcarriers are phase-modulated by the signals to be treated, or pulse multiplexing, in which case, with three primary colour signals, the modulation concerns the front and rear flanks of one pulse, respectively, by two of the signals to be modulated and the amplitude of this pulse is modulated by the third signal.

Of course, the invention is not restricted to colour television cameras, but may also be applied, for example, to apparatus for mixing the signals of several pictures.

What is claimed is:

1. A colour television camera comprising: analysing means for providing at least two primary colour signals; time multiplexing means having at least two inputs for receiving said signals and an output for supplying a resultant signal; a single channel within said camera connected to said output for the treatment and the transmission of said resultant signal, said channel having an output for supplying a treated resultant signal; and time demultiplexing means connected to said output of said channel and having at least two outputs for supplying treated primary colour signals corresponding to said primary colour signals.

2. A colour television camera comprising: analysing means for providing at least three primary colour signals; three first gates, having respective control inputs, for passing respectively said primary colour signals upon a control signal being applied in parallel to said control inputs; a single channel having an input connected to said first gates for the treatment and the transmission of the signals transmitted by said three gates; three second gates, having respective control inputs, respectively connected to said control inputs of said first gates and respective inputs connected to said channel; and a sampling pulse generator having three outputs respectively connected to said control inputs of said first and second gates for supplying at each of said generator outputs sampling pulses time-shifted with respects to those supplied at the other outputs.

3. A colour television camera as claimed in claim 2, wherein said analysing means further provide a wideband high definition luminance signal and said pulse generator supplies pulses at the same frequency to each of said three outputs, said frequency being higher than the higher frequency of the frequency band of said primary colour signals.

4. A colour television camera as claimed in claim 2, wherein said analysing means provide three primary colour signals R, G and B, and said sampling pulses supplied to said control input of said first and second gates corresponding to said signal G have a frequency double the frequency of said sampling pulses supplied to the others of said gates.

References Cited UNITED STATES PATENTS 2,951,903 9/1960 Devrijer 1785.2 3,392,231 7/1968 Schonfelder. 3,431,351 3/1969 Scnnhenn 178-5.2

RICHARD MURRAY, Primary Examiner ALFRED H. EDDLEMAN, Assistant Examiner 

